The human heart is comprised of four major chambers with two ventricles and two atria. Generally, the right-side heart receives oxygen-poor blood from the body into the right atrium and pumps it via the right ventricle to the lungs. The left-side heart receives oxygen-rich blood from the lungs into the left atrium and pumps it via the left ventricle to the aorta for distribution throughout the body. Due to any of a number of illnesses, including coronary artery disease, high blood pressure (hypertension), valvular regurgitation and calcification, damage to the heart muscle as a result of infarction or ischemia, myocarditis, congenital heart defects, abnormal heart rhythms or various infectious diseases, the left ventricle may be rendered less effective and thus unable to adequately pump oxygenated blood throughout the body.
The Centers for Disease Control and Prevention (CDC) estimates that about 5.1 million people in the United States suffer from some form of heart failure. Heart failure is generally categorized into four different stages with the most severe being end stage heart failure. End stage heart failure may be diagnosed where a patient has heart failure symptoms at rest in spite of medical treatment. Patients at this stage may have systolic heart failure, characterized by decreased ejection fraction. In patients with systolic heart failure, the walls of the ventricle are weak and do not squeeze as forcefully as a healthy patient. Consequently, during systole a reduced volume of oxygenated blood is ejected into circulation, a situation that continues in a downward spiral until death. Patients may alternatively have diastolic heart failure wherein the heart muscle becomes stiff or thickened making it difficult for the affected chamber to fill with blood. A patient diagnosed with end stage heart failure has a one-year mortality rate of approximately 50%.
For patients that have reached end stage heart failure, treatment options are limited. In addition to continued use of drug therapy commonly prescribed during earlier stages of heart failure, cardiac transplantation and implantation of a mechanical assist device are typically recommended. While a cardiac transplant may significantly prolong the patient's life beyond the one year mortality rate, patients frequently expire while on a waitlist for months and sometimes years awaiting a suitable donor heart. Presently, the only alternative to a cardiac transplant is a mechanical implant. While in recent years mechanical implants have improved in design, typically such implants will prolong a patient's life by a few years at most, and include a number of co-morbidities.
One type of mechanical implant often used for patients with end stage heart failure is a left ventricular assist device (LVAD). The LVAD is a surgically implanted pump that draws oxygenated blood from the left ventricle and pumps it directly to the aorta, thereby off-loading (reducing) the pumping work of the left ventricle. LVADs typically are used either as “bridge-to-transplant therapy” or “destination therapy.” When used for bridge-to-transplant therapy, the LVAD is used to prolong the life of a patient who is waiting for a heart transplant. When a patient is not suitable for a heart transplant, the LVAD may be used as a destination therapy to prolong the life, or improve the quality of life, of the patient, but generally such prolongation is for only a couple years.
One type of LVAD is a reciprocating pump such as U.S. Pat. No. 4,277,706 to Isaacson, entitled “Actuator for Heart Pump.” The pump described in the Isaacson patent includes a housing having an inlet and an outlet, a cavity in the interior of the pump connected to the inlet and the outlet, a flexible diaphragm that extends across the cavity, a plate secured to the diaphragm, and a ball screw that is configured to be reciprocated to drive the plate and connected diaphragm from one end of the cavity to the other end to simulate systole and diastole. The ball screw is actuated by a direct current motor. The Isaacson patent also describes a controller configured to manage the revolutions of the ball screw to control the starting, stopping and reversal of directions to control blood flow in and out of the pump.
LVADs utilizing rotary, centrifugal and axial configurations also are known. For example, U.S. Pat. No. 3,608,088 to Reich, entitled “Implantable Blood Pump,” describes a centrifugal pump to assist a failing heart. The Reich patent describes a centrifugal pump having an inlet connected to a rigid cannula that is coupled to the left ventricular cavity and a Dacron graft extending from the pump diffuser to the aorta. The pump includes an impeller that is rotated at high speeds to accelerate blood, and simulated pulsations of the natural heart by changing rotation speeds or introducing a fluid oscillator.
U.S. Pat. No. 5,370,509 to Golding, entitled “Sealless Rotodynamic Pump with Fluid Bearing,” describes a centrifugal blood pump capable for use as a heart pump. One embodiment described involves a blood pump with impeller blades that are aligned with the axes of the blood inlet and blood outlet. U.S. Pat. No. 5,588,812 to Taylor, entitled “Implantable Electrical Axial-Flow Blood Pump,” describes an axial flow blood pump. The pump described in the Taylor patent has a pump housing that defines a cylindrical blood conduit through which blood is pumped from the inlet to the outlet, and rotor blades that rotate along the axis of the pump to accelerate blood flowing through the blood conduit.
Pumps other than the rotary and positive displacement types are known in the art for displacing fluid. For example, U.S. Pat. Nos. 6,361,284 and 6,659,740, both to Drevet, entitled “Vibrating Membrane Fluid Circulator,” describe pumps in which a deformable membrane is vibrated to propel fluid through a pump housing. In these patents, vibratory motion applied to the deformable membrane causes wave-like undulations in the membrane that propel the fluid along a channel. Different flow rates may be achieved by controlling the excitation applied to the membrane.
U.S. Pat. No. 7,323,961 to Drevet, entitled “Electromagnetic Machine with a Deformable Membrane”, describes a device in which a membrane is coupled in tension along its outer edge to an electromagnetic device arranged to rotate about the outer edge of the membrane. As the electromagnetic device rotates, the outer edge of the membrane is deflected slightly in a direction normal to the plane of the membrane. These deflections induce a wave-like undulation in the membrane that may be used to move a fluid in contact with the membrane.
U.S. Pat. No. 9,080,564 to Drevet, entitled “Diaphragm Circulator,” describes a tensioned deformable membrane in which undulations are created by electromechanically moving a magnetized ring, attached to an outer edge of a deformable membrane, over a coil. Axial displacement of magnetized ring causes undulations of membrane. Like in the '961 patent, the membrane undulations can be controlled by manipulating the magnetic attraction. U.S. Pat. No. 8,714,944 to Drevet, entitled “Diaphragm pump with a Crinkle Diaphragm of Improved Efficiency” and U.S. Pat. No. 8,834,136 to Drevet, entitled “Crinkle Diaphragm Pump” teach similar types of vibrating membrane pumps.
Notwithstanding the type of LVAD device employed, an LVAD generally includes an inflow cannula, a pump, and an outflow cannula, and is coupled to an extracorporeal battery and control unit. The inflow cannula typically directly connects to the left ventricle, e.g., at the apex, and delivers blood from the left ventricle to the pump. The outflow cannula typically extends outside of the heart and includes an extra-cardiac return line that is routed through the upper chest and connects to the aorta distal to the aortic valve. As such the outflow cannula delivers blood from the pump to the aorta via the return line, which typically consists of a tubular structure, such as a Dacron graft, that is coupled to the aorta via an anastomosis.
A sternotomy or thoracotomy is required to implant the pump within the patient. In addition, a separate aortic anastomosis procedure is also required to connect the pump to the aorta. The return line that delivers oxygen-rich blood to the aorta significantly reduces efficiency of the system. Additionally, when the pump is operated in a pulsatile mode the return line that connects the pump to the aorta should incorporate an artificial valve or require the pump to run continually to prevent backflow, thus increasing the risk of barotrauma to the blood. The return line also creates issues with possible kinking caused by chest compression. The increased foreign surface area of the return line also can lead to undesired platelet activation and thrombosis.
What is needed is an energy efficient implantable pump having light weight, small size, and a delivery mechanism for delivering blood to the aorta with minimal blood damage.